Heat-resistant film and composite ion-exchange membrane

ABSTRACT

The present invention is a heat-resistant film comprising at least any one of a polybenzazole, aramid and polyamideimide produced by introducing a thin film made by a roll, slit or press from a polymer solution sandwiched between at least two supports into a coagulating bath and peeling the supports off in the coagulating bath to effect the coagulation, and a composite ion-exchange membrane having a surface layer consisting of an ion-exchange resin excluding a porous film on the both side of a composite layer formed by impregnating said film with the ion-exchange resin. A heat-resistant film having a combination of excellent heat resistance, mechanical strength, smoothness and interlaminar peeling resistance, especially a microporous heat-resistant film, and a composite ion-exchange membrane employing the same which has an excellent ion conductivity are provided.

TECHNICAL FIELD

The present invention relates to a film made from a heat-resistantpolymer such as polybenzazole, which has a combination of excellent heatresistance, mechanical strength, smoothness and interlaminar peelingresistance, especially a microporous film. The present invention alsorelates to a composite ion-exchange membrane whose mechanical strengthand ion conductivity are excellent, especially a polymeric solidelectrolyte membrane.

BACKGROUND ART

Recently, a rapid advancement in IT field poses also to a non-porous orporous film employed as a part of its related electronic instrument orcells a severe commercial requirement with regard to heat resistance,chemical resistance, size stability, thickness accuracy, uniformity andprice in response to the requirement for a higher performance or asmaller size of such an instrument or cell.

For example, a super engineering plastic such as polybenzazole,polyimide, aramid and the like is excellent in terms of heat resistance,chemical resistance, irradiation resistance and the like, and is a veryattractive film material capable or fulfilling the commercialrequirement described above. However, such a super engineering plastichas an extremely high melting point and a decomposition temperaturewhich is extremely close to the melting point which make it difficult touse a so called fusion film-forming technology, and a solutionfilm-forming technology is employed generally.

Such a solution film-forming technology is a film forming method inwhich a solution of a resin in a solvent is extruded via a die as a thinfilm which is applied on an endless belt and dried or coagulated andthen peeled off as disclosed in many patent publications such asJP-A-2001-151902, JP-A-2002-283369, JP 3183297, JP-A-2001-151910, JP3196684 and the like. As a method for improving a disadvantageous natureof the application onto an endless belt described above which is a filmsurface defect resulting from the pinhole formation due to an erosion ordamage of a metal belt attributable to repetitive drying and/orcoagulation and peeling, a method for producing a film consisting of aheat-resistant resin by applying a resin solution onto a biaxiallyoriented polyester film followed by a drying step followed by peelingthe coating film from the polyester film is disclosed inJP-A-2000-233439.

However, any of the production methods described above involves aproblem resulting from the use of a die for forming a thin film which isexperienced as a difficulty in applying a film-forming solution whoseviscosity is departing from an appropriate range as well as a limitedaccuracy of the thickness of the resulting film. Moreover, drying andcoagulating behaviors are different between the supported side of thethin film and the opposite side since only one side of the thin filmsubjected to the steps of drying and/or coagulation is supported by abelt or polyester film, resulting in a problematic difference in thecharacteristics or the structure between the both sides of a resultantfilm. Furthermore, the need of expensive devices such as dies andextruders is disadvantageous from an economical point of view. Inaddition, such a use of the dies and extruders requires a large amountof a solution or solvent for replacing a resin solution or for washingthe devices, which is also disadvantageous from an economical point ofview, and also poses a problematic inconvenience in switching the itemsrequired for responding a diversity of commercial needs, thus raising astrong desire to develop a production method capable of solving such aproblem.

On the other hand, a solution of a rigid polymer at a high concentrationtends to form a liquid crystal phase showing an optical anisotropy.Since such a rigid polymer solution tends to undergo an orientation ofmolecular chains in the direction of flowing, it takes a long time untilthe direction of the molecular chain, once aligned, becomes random.Accordingly, the film forming method described above gives a substantialdifference in the dynamic characteristics between the direction in whichthe polymer solution is, extruded and extended and the directionvertical thereto, which should be improved. Nevertheless, as describedin Chapter 3 in Application of High Temperature Polymers, ed. by RobertR. Luise, CRC Press, 1997, the molecules are aligned in an extrudingdirection and a draw-down direction, and thus give a problematic filmwhich is readily torn apart when being pulled in the lateral direction.Accordingly, U.S. Pat. No. 2,898,924 employed a technology for producinga thin film by means of a biaxial orientation using a blow moldingmethod, and U.S. Pat. No. 4,939,235 attempted to improve the anisotropyof the dynamic characteristics by means of an orientation in differentdirections between the both sides of a film.

However, any of these rigid polymers allows, when subjected to a biaxialorientation or an orientation to different directions between the bothsides of a film, a molecular chain to readily undergo a so-calledintra-plane orientation, resulting in a problematic tendency to undergointerlaminar peeling or brittle destruction in the direction of the filmthickness.

While any of the methods described above focused on the characteristicsof the sheer viscosity upon processing which is reduced relatively at ahigh concentration which allows a solution of a rigid polymer to exhibitan optical anisotropy, i.e., liquid crystal property, a film formationusing a solution exhibiting an optical anisotropy involves a difficultyin balancing the mechanical properties between the longitudinaldirection of the film (MD, direction of film running, machine direction)and the widthwise direction (TD, direction vertical to MD, transversedirection), and also poses a problem of the interlaminar peeling in thedirection of the film thickness as described above. As a method forsolving a problem with regard to the balance of the dynamiccharacteristics, a method for forming a film by conducting a dieextrusion and previous steps in an optically anisotropic phase and theneffecting a phase transition to an optically isotropic phase after thedie extrusion step by means of composition change or temperature changeis disclosed in JP-A-9-118758. In addition, JP-A-2000-273214 discloses amethod equivalent to the method disclosed in JP-A-9-118758, i.e., amethod for producing a polybenzazole film exhibiting a high elasticityand an appropriate extension which is obtained by rolling apolybenzazole solution showing an optical anisotropy onto a supportfollowed by changing into an optically isotropic condition.

However, in any of the methods described above, a film formed from aliquid crystalline anisotropic solution undergoes the formation of anorientation spot due to the polydomain structure of the liquid crystalphase and tends to be heterogeneous, and still involves aproblematically interlaminar peeling in the direction of the filmthickness. Also the problems of the unbalance of the mechanicalproperties between the longitudinal and widthwise directions are notsolved satisfactorily.

In order to overcome such a disadvantage, a processing from a solutionat a low concentration is required, and a method for forming a film froma solution at a low concentration by means of a spin coating method wasattempted. For example, L. A. Cintavey et al describes in Journal ofApplied Polymer Science, Vol. 76, pp 1448-1456 (2000) a polybenzazolethin film formed on a silicon wafer using a 0.5% solution of apolyphenylene benzobisthiazole in methanesulfonic acid, whose opticalcharacteristics are also discussed. However, this method poses adifficulty in obtaining a large amount of films at once by this method,and thus is not preferable from an industrial point or view. The filmforming method using a die described above also involves a problem whichis a difficulty in utilizing a processing from a solution at a lowconcentration a film forming solution because of a too low viscosity,which problem should also be solved.

An aramid film also involves the problems similar to those associatedwith a polybenzaole film, and is actually industrialized by an extremelycomplicated process.

A polyamideimide film is also studied in JP-A-7-41559, JP-A-10-226028,JP-A-11-216344, JP-A-2001-151902, JP-A-2002-283369, JP 3183297,JP-A-2001-151910, JP 3196684, JP-A-2000-23339, but a polyamideimide filmhaving excellent thickness accuracy and uniformity has not been obtainedat an acceptable cost.

On the other hand, a novel electricity generation technology is focusedon recently which is excellent in terms of energy efficiency andenvironmental protection. Especially, a solid polymer fuel cellemploying a polymeric solid electrolyte membrane is subjectedextensively to the development of an electric power supply device in anautomobile or disperse electricity generation because of its propertiessuch as a high energy density and a lower operation temperature whencompared with other modes of the fuel cells which allow the start-up andshut-off to be accomplished readily. Similarly, a direct methanolic fuelcell employing a polymeric solid electrolyte membrane and a directsupply of methanol as a fuel is also developed extensively for theapplications to power supplies for portable devices. The polymeric solidelectrolyte membrane usually employs a proton-conductive ion-exchangeresin. In addition to the proton conductivity, other properties such asa fuel permeation preventing ability for preventing the permeation of afuel such as hydrogen and a mechanical strength should be possessed bythe polymeric solid electrolyte membrane. A known polymeric solidelectrolyte membrane may for example be a perfluorocarbonsulfonic acidpolymer membrane incorporating a sulfonate group such as “Nafion®”(trade name) manufactured by DuPont in the United States of America.

For the purpose of achieving a high output or high efficient of a solidpolymeric fuel cell, a reduction in the ion conductivity resistance ofthe solid polymeric fuel cell is effective, and can be accomplished forexample by reducing the film thickness. Even in the case of a polymericsold electrolyte membrane such as Nafion®, the film thickness isattempted to be reduced. However, the reduction in the film thicknessleads to a reduction in the mechanical strength, which may allow themembrane to be readily broken upon adhesion of the polymeric solidelectrolyte membrane and an electrode by a hot press, or may result in aproblematic deterioration of the electricity generation characteristicsdue to the peeling of the electrode, once being adhered to the polymericsolid electrolyte membrane, due to the change in the membrane size.Furthermore, the reduction in the film thickness reduces the fuelpermeation preventing ability, resulting in a problematic reduction inthe power generation ability or in the fuel utilization efficiency.

Uses of a polymeric solid electrolyte membrane in addition to the use asan ion-exchange membrane for a fuel cell described above may for examplebe a use in an electrochemical field including an electrolysis such asan alkaline electrolysis or production of hydrogen from water as well asan electrolyte in various cells such as a lithium cell or a nickelhydrogen cell, a use in a mechanically functional material such as amicro actuator or artificial muscle, as well as other wide range of theuse including an ion or molecule recognizing/responding functionalmaterial, separating/purifying functional material and the like, andthus is expected in each use to be capable of providing an excellentfunction which has not been achieved so far by means of enabling ahigher strength and a thinner thickness of the polymeric solidelectrolyte membrane.

As a means for improving the mechanical strength of a polymeric solidelectrolyte membrane while suppressing the change in the size, acomposite polymeric solid electrolyte membrane is proposed whichcombines a polymeric solid electrolyte membrane with various reinforcingmaterials. JP-A-8-162132 describes a composite polymeric solidelectrolyte membrane in which an oriented porous polytetrafluoroethylenefilm are impregnated and integrated with an ion-exchange resinperfluorocarbonsulfonic acid polymer being filled in its voids. However,since in such a composite polymeric solid electrolyte membrane thereinforcing material is made from a polytetrafluoroethylene, thereinforcing material is softened by heat upon generating electricity toundergo a change in the size via a creep, and also since the capacity ofthe voids in the reinforcing material undergoes almost no change upondrying after impregnating the reinforcing material with a solution of aperfluorocarbonsulfonic acid polymer, the perfluorocarbonsulfonic acidpolymer precipitating inside of the voids of the reinforcing materialtends to be localized, and for the purpose of filling the voidscompletely with the polymer a complicated process such as impregnationwith an ion-exchange resin solution followed by drying which should berepeated several time, and also since the voids tend to remain as theyare it is difficult to obtain a film having an excellent fuel permeationpreventing ability. JP-A-2001-35508 describes a composite polymericsolid electrolyte membrane in which a fibrillatedpolytetrafluoroethylene is dispersed as a reinforcing material in a filmof a perfluorocarbonsulfonic acid polymer. However, such a compositepolymeric solid electrolyte membrane does not have a sufficientmechanical strength due to the non-continuous structure of thereinforcing material and undergoes a problematic peeling of an electrodedue to an inability of suppressing the deformation of the membrane.

A polybenzazole such as a polybenzoxazole (PBO) or polybenzimidazol(PBI) (hereinafter simply referred to as polybenzazole) is excellent interms of a high heat resistance, a high strength and a high elasticity,and accordingly expected to be suitable as a reinforcing material for apolymeric solid electrolyte membrane.

JP-A-2000-273214 discloses a method in which a film of a solution of apolybenzazole which is optically anisotropic is formed and then madeisotropic by moisture absorption followed by coagulation wherebyobtaining a polybenzazole film, but a polybenzazole film obtained by thedescribed method is a transparent and highly dense film, which is notsuitable for the purpose of impregnating it with an ion-exchange resinto give an ion-exchange membrane.

In a molding process of a polybenzazole, a film formation by a rollingmethod using an applicator is well known. However, when using apolybenzazole solution whose polymer concentration is 1% by weight orhigher, the polybenzazole solution becomes highly viscose, resulting ina formation of streaks in the direction of a squeegee, which leads to adifficulty in obtaining a smooth film. The polymer concentration whichcan practically be employed is 0.5% by weight at maximum. Accordingly, apoor economical performance and insufficient strength and elasticity ofthe resultant film are experienced unfortunately. A film made from apolybenzazole by a rolling method has a surface structure on the side incontact with a support which is different from the surface structure onthe side not in contact with a support, whereby presenting an asymmetricstructure. While the surface in contact with the support exhibits adense structure, the surface not in contact with the support exhibits aporous structure. When such a asymmetrically structured polybenzazolesupport film is impregnated with an ion-exchange resin, a sufficientimpregnation with the ion-exchange resin is not achieved at the regionwhere the dense structure is formed, resulting in a problematicallyinsufficient electricity generating ability of a resultant ion-exchangemembrane.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: a schematic view of a production method of the presentinvention.

FIG. 2: a schematic view of a interlaminar peeling test.

FIG. 3: a schematic view of a sectional structure of a compositeion-exchange membrane.

In Figures, 1 is a resin solution supply pipe, 2 is a resin solution, 3is a support 1, 4 is a support 2, 5 is a support 1 unwinding roll, 6 isa support 2 supplying role, 7 is a counter roll, 8 is a laminated bodyconsisting of support/resin solution/support, 9 is a wet resin film, 10is a wet resin film winding roll, 11 is a support 2 winding roll, 12 isa support 1 winding roll, 13 is a coagulation bath, 14 is a test film,15 is an adhesive tape, 16 is a surface layer A, 17 is a composite layerand 18 is a surface layer B.

DISCLOSURE OF THE INVENTION

The present invention solves the problems associated with a prior artdescribed above and provides a film made from a heat-resistant polymersuch as polybenzazole, which has a combination of excellent heatresistance, mechanical strength, smoothness and interlaminar peelingresistance, especially a microporous film. The present invention alsoprovides a composite ion-exchange membrane whose mechanical strength andion conductivity are excellent, especially a polymeric solid electrolytemembrane.

The present invention is characterized in that it is produced byintroducing a thin film made by a roll, slit or press from a polymersolution sandwiched between at least two supports into a coagulatingbath and peeling the supports off in the coagulating bath to effect thecoagulation. An inventive composite ion-exchange membrane ischaracterized by the formation of a composite layer by impregnating aporous film made from a polybenzazole described above with theion-exchange resin and a surface layer consisting of an ion-exchangeresin having no micropores formed on the both side of said compositelayer as sandwiching said composite layer.

Thus, the present invention is: (1) a heat-resistant film comprising atleast any one of a polybenzazole, aramid and polyamideimide produced bysandwiching a polymer solution between at least two supports,introducing a laminate, obtained by converting the polymer solution intoa thin film by a roll, slit or press, into a coagulating bath andpeeling at least one side of the supports off in the coagulating bathwhereby effecting the coagulation of a polymer solution in the form ofthe thin film;

(2) a heat-resistant film according to the above-mentioned (1) whereinthe polymer solution is an isotropic solution;

(3) a heat-resistant film according to the above-mentioned (1) or (2)wherein the coagulation bath is a poor solvent for the polymer, or amixture of a poor solvent and a good solvent, or a solution containingsalts in a poor solvent;

(4) a heat-resistant film according to any of the above-mentioned 1 to 3wherein the support is a film allowing the poor solvent for the polymerin the coagulation bath or a vapor thereof to permeate and wherein thepoor solvent or a vapor thereof which has permeate said film is used foreffecting at least a part of the coagulation of the polymer solution;and

(5) a composite ion-exchange membrane comprising a composite layerformed by impregnating a heat-resistant film according to any of theabove-mentioned (1) to (4) with the ion-exchange resin and a surfacelayer consisting of an ion-exchange resin having no micropores formed onthe both side of said composite layer as sandwiching the compositelayer.

A heat-resistant film and a composite ion-exchange membrane according tothe present invention are detailed below.

A polymer constituting an inventive heat-resistant film is a polymerwhich is dissolved in a solvent and which has a film-forming ability,and is a polymer consisting of at least one of a polybenzazole, aramidand polyamideimide whose polymer melting points are extremely high andwhose decomposition temperatures are extremely close to the meltingpoints, i.e. one classified as a so-called super engineering plastic.

A polybenzazole employed in the present invention is a polymer having astructure containing in its polymer chain an oxazole ring, thiazole ringor imidazole ring, and means one containing in its polymer chain arepeating unit represented by Formulae (1-1, -2) shown below.

In Formulae, each of Ar₁, Ar₂ and Ar₃ denotes an aromatic unitoptionally substituted with various aliphatic groups, aromatic groups,halogen group, hydroxyl group, nitro group, cyano group, trifluoromethylgroup and the like. Such an aromatic unit may be a monocyclic unit suchas a benzene ring, a fused cyclic unit such as naphthalene, anthraceneand pyrene, or a polycyclic aromatic unit of two or more such aromaticunits taken together via any bonds. The positions of N and X in anaromatic unit are not limited particularly as far as they allow abenzazole ring to be formed. Furthermore, it may be a heterocyclicaromatic unit having N, O or S in the aromatic ring, in addition to ahydrocarbon-based aromatic unit. X denotes O, S or NH.

Ar₁ described above is preferably represented by Formulae (2-1, -2)shown below.

In Formulae, each of Y₁ and Y₂ denotes CH or N, Z is a direct bond, —O—,—S—, —SO₂—, —C(CH₃)₂—, —C(CF₃)₂— and —CO—.

Ar₂ is preferably represented by Formulae (3-1, -22) shown below.

In Formulae, W denotes —O—, —S—, —SO₂—, —C(CH₃)₂—, —C(CF₃)₂— and —CO—.

Ar₃ is preferably represented by Formula (4) shown below.

While such a polybenzazole may be a homopolymer having a repeating unitdescribed above, it may be a random, alternating or block copolymerhaving a combination of the structure units listed above, such as thosedescribed in U.S. Pat. No. 4,703,103, U.S. Pat. No. 4,533,692, U.S. Pat.No. 4,533,724, U.S. Pat. No. 4,533,693, U.S. Pat. No. 4,539,567, U.S.Pat. No. 4,578,432 and the like.

Typically, such a polybenzazole structure unit may be those representedby Formulae (5-1 to -8, 6-1 to -8, 7-1 to -12, 8-1 to -8, 9-1 to -8,10-1 to -12, 11-1 to -11).

In addition to only these polybenzazole structure units, other polymerstructure units may be employed to form a random or block copolymer. Insuch a case, other polymer structure units are selected preferably fromhighly heat-resistant aromatic structure units. Typically, a polyimidestructure unit, polyamide structure unit, polyamideimide structure unit,polyoxydiazole structure unit, polyazomethine structure unit,polybenzazoleimide structure unit, polyether ketone structure unit andpolyethersulfone structure unit may be exemplified.

A polyimide structure unit may for example be one represented by Formula(12) shown below.

In Formula, Ar₄ is represented by a tetravalent aromatic unit, which ispreferably one represented by Formulae (13-1 to -8) shown below.

Ar₃ is a divalent aromatic unit, which is preferably one represented byFormulae (14-1 to -8) shown below. On an aromatic ring shown here,various substituents may be present such as a methyl group, methoxygroup, halogen group, trifluoromethyl group, hydroxyl group, nitrogroup, cyano group and the like.

Typically, such a polyimide structure unit may be one represented byFormulae (15-1 to 8, 16-1 to -5) shown below.

A polyamide structure unit may for example be one represented byFormulae (17-1, -2) shown below.

In Formulae, Ar₆, Ar₇ and Ar₈, independently of one another, areselected preferably from Formulae (18-1 to -6) shown below. On anaromatic ring shown here, various substituents may be present such as amethyl group, methoxy group, halogen group, trifluoromethyl group,hydroxyl group, nitro group, cyano group and the like.

Typically, a polyamide structure unit may for example be one representedby Formulae (19-1 to -4) shown below.

A polyammideimide structure unit may for example be one represented byFormula (20) shown below.

In Formula, Ar₉ is preferably selected from the examples of thestructure of Ar₅ listed above.

Typically, a polyamideimide structure unit may for example be onerepresented by Formulae (21-1, -2) shown below.

A polyoxydiazole structure unit may for example be one represented byFormula (22) shown below.

In Formula, Ar₁₀ is preferably selected from the examples of thestructure of Ar₅ listed above.

Typically, a polyoxydiazole structure unit may for example be onerepresented by Formulae shown below.

A polyazomethine structure unit may for example be one represented byFormula (24) shown below.

In Formula, each of Ar₁₁ and Ar₁₂ is preferably selected from theexamples of the structure of Ar₆ listed above.

Typically, a polyazomethine-based structure unit may for example be onerepresented by Formulae (25-1 to -5) shown below.

Such a polybenzazoleimide structure unit may for example be onerepresented by Formula (26) shown below.

In Formulae, each of Ar₁₃ and Ar₁₄ is preferably selected from theexamples of the structure of Ar₄ listed above.

Typically, such a polybenzazoleimide structure unit may for example beone represented by Formulae (27-1, -2) shown below.

A polyether ketone structure unit and a polyether sulfonic acid unitgenerally have structures having aromatic units linked via ketone bondsor sulfone bonds together with ether bonds, and contain the structurecomponents selected from Formulae (28-1 to -6) shown below.

In Formulae, Ar₁₅ to Ar₂₃ independently from one another preferablydenote those represented by Formulae shown below. On an aromatic ringshown here, various substituents may be present such as a methyl group,methoxy group, halogen group, trifluoromethyl group, hydroxyl group,nitro group, cyano group and the like.

Typically, a polyether ketone structure unit may for example be onerepresented by Formulae (30-1 to 8) shown below.

An aromatic polymer structure unit copolymerizable with such apolybenzazole structure unit does not strictly mean a repeating unitwithin a polymer chain, and rather means a structure unit capable ofcoexisting with the polybenzazole structure unit within a polymer mainchain. Such a copolymerizable aromatic polymer structure unit may becopolymerized alone or in combination of two or more. In order tosynthesize such a copolymer, an amino group, carboxyl group, hydroxylgroup, halogen group and the like may be introduced into the unitterminal consisting of benzazole structure units and may serve as areactant of such an aromatic synthesis, or a carboxyl group isintroduced into the unite terminal containing such aromatic structureunites and allowed to serve as a reactant of the polybenzazole synthesisto be polymerized.

A polybenzazole described above is subjected to a condensationpolymerization in a polyphosphoric acid solvent to give a polymer. Thepolymerization degree of the polymer is represented as a limitingviscosity, which is preferably 15 dl/g or higher, more preferably 20dl/g or higher. A degree below this range leads to a problematicallyreduced strength of a film obtained. The limiting viscosity ispreferably 35 dl/g or lower, more preferably 26 dl/g or lower. A degreehigher above this range leads to an elevated viscosity of the solution,which makes a processing difficult and puts a limitation on theconcentration of a polybenzazole solution capable of forming anisotropic solution, resulting in a problematic difficulty in forming afilm under an isotropic condition. These solutions are employed aspolymer solutions after diluting them with solvents such aspolyphosphoric acid, methanesulfonic acid and the like.

A porous film of a polybenzazole of the present invention is formed bysteps for extruding and thinning, coagulating, washing and drying thefilm. As a means for obtaining a uniform porous structure, a methodinvolving a contact with a poor solvent to effect the coagulation isemployed. A poor solvent is a solvent miscible with a solvent for apolymer solution and may be either in a liquid phase or a gas phase. Itis also preferable to use a combination of the coagulation by a poorsolvent in a gas phase and the coagulation by a poor solvent in a liquidphase. While a poor solvent employed for a coagulation may for examplebe water, an aqueous solution of an acid or an aqueous solution of aninorganic salt as well as an organic solvent such as alcohols, glycols,glycerin and the like, the poor solvent employed for the coagulationshould carefully be selected since some combination with a polybenzazolesolution employed may cause problems such as a reduction in the surfaceporosity or the void ratio of a porous film or a non-continuous cavityformation inside of the porous film. In the coagulation of an isotropicpolybenzazole solution according to the present invention, the filmsurface and internal structure and the void ratio can be controlled byselecting a poor solvent together with the coagulation condition fromwater vapor, aqueous solution of methanesulfonic acid, aqueous solutionof phosphoric acid, aqueous solution of glycerin, as well as aqueoussolutions of inorganic salts such as aqueous solution of magnesiumchloride. An especially preferred coagulation means is a coagulation bycontact with water vapor, coagulation by contact with water vapor for ashort period at an early stage of the coagulation followed by contactwith water, and coagulation by contact with an aqueous solution ofmethanesulfonic acid.

A method for forming a film of a polybenzazole solution according to thepresent invention is most preferably a procedure comprising introducinga thin film made by a roll, slit or press from a polymer solutionsandwiched between at least two supports into a coagulating bath andpeeling the supports off in the coagulating bath to effect thecoagulation. As used herein, the thin film formation is to adjust thethickness generally at 10 μm to 500 μm in the pre-coagulation polymersolution state by employing the means described above, although thethickness may vary depending on the commercial demand. The structure andthe arrangement of the roll, slit or press may be in variouscombinations. It is desirable to use a method in which a polymersolution sandwiched between at least two supports is sandwiched betweenat least two rolls and the rolls facing each other are rotated indifferent directions to feed the polymer solution in the form of a thinfilm.

The supports sandwiching the polymer solution being rolled is introducedvia a guide roll into the coagulation bath, where they are peeled offwhereby effecting the coagulation of the polymer solution to give aporous membrane. Prior to a complete coagulation of the polymer solutionby peeling the supports in the coagulation bath, the polybenzazole iscoagulated at least partly by a poor solvent or a vapor thereof whichhad been permeated through the supports, whereby controlling the filmsurface and internal structure and the void ratio.

The outermost support and the polymer solution here may sandwich aporous support, fabric or nonwoven fabric to form a composite membrane.The porous support, fabric or nonwoven fabric may be used directly as asupport to form a composite membrane. The porous support, fabric ornonwoven fabric is preferably gas permeable or liquid permeable one. Asupport allowing a poor solvent for the polybenzazole or a vapor thereofto permeate is preferably a porous support made from a polypropylene,and otherwise porous supports made from various materials such aspolyethylene and polytetrafluoroethylene can also be employed.Especially when using water or a solvent mixture of water with othersolvent or aqueous solution as a coagulation solution, a porous supportsenabling the permeation only of water vapor while preventing thepermeation of water in the liquid phase is employed preferably. It mayfor example be a commercial membrane filter purported to have a poresize of 0.03 μm to 10 μm and a separator film for a cell.

As used herein, a coagulation bath means not only a tank containing acoagulation solution but also a zone where a gas, mist or vapor having acoagulating ability exists. A coagulation solution may for example bewater, aqueous solution of metal salt, polyhydric alcohol, aprotic polarsolvent, protic polar solvent as well as aqueous solutions ofpolyphosphoric acid and methanesulfonic acid which are solution-dilutingsolvents. A mist or vapor of these solution is also included. Thetemperature of the coagulation solution is preferably 10° C. or higherand 70° C. or lower. More preferably, the temperature is 30° C. orhigher and 60° C. or lower. Generally, a membrane structure may varydepending on the balance between the migration of the coagulationsolution into the polymer solution film and the effluent of the polymersolvent from the polymer solution thin film. An excessively lowtemperature of the coagulation solution leads to an insufficientliquid-liquid exchange between the coagulation solution and the polymersolvent, resulting in a difficulty in obtaining a desired filmstructure. An excessively high temperature of the coagulation solutionbasically provides a desired structure, but the strength is necessarilyreduced to a substantial extent. In the present invention, thecoagulation temperature is preferably 10° C. or higher and 70° C. orlower. More preferably, a temperature of 30° C. or higher and 60° C. orlower serves to provide a porous membrane whose structure and strengthare both satisfactory.

A polybenzazole solution employed in the present invention should beformed into a film using a composition under an isotropic condition forthe purpose of obtaining a uniform porous film having a large voidratio, and a preferred range of the concentration of a polybenzazolesolution is 0.3% by weight or higher, more preferably 0.5% by weight orhigher, further preferably 0.8% by weight or higher. A concentrationlower than this range may give a reduced viscosity of the polymersolution, which leads to a difficulty in molding and is disadvantageousfrom an economical point of view and also leads to a problematicallyreduced strength of the porous membrane. The range of the concentrationis further preferably 3% by weight or less, more preferably 2% by weightor less, and especially 1.5% by weight or less. A concentration higherthan this range may give a problematic anisotropy depending on thepolymer composition or the polymerization degree of the polybenzazole. Aporous membrane formed from an optically anisotropic polybenzazolesolution is not preferable since a porous polybenzazole film havingcontinuous voids at a high void ratio which allows a large amount of anion-exchange resin to be impregnated.

For adjusting the concentration of a polybenzazole solution within therange specified above, the following procedure may be taken. Thus, amethod in which a polymer solid is once separated from a polymerizedpolybenzazole solution which is combined with a solvent again anddissolved whereby adjusting the concentration, a method in which withoutseparating a polymer solid from a polymer solution just being subjectedto a condensation polymerization in polyphosphoric acid the polymersolution is combined with a solvent for dilution whereby adjusting theconcentration, and a method in which a polymer solution at aconcentration within the specified range is directly obtained byadjusting the polymerization composition of the polymer arecontemplated.

A solvent employed preferably for adjusting the concentration of apolymer solution may for example be methanesulfonic acid,dimethylsulfuric acid, polyphosphoric acid, sulfuric acid,trifluoroacetic acid and the like, which may be employed in combinationas a solvent mixture. Those especially preferred are methanesulfonicacid and polyphosphoric acid.

A porous film made from a polybenzazole thus coagulated is preferablywashed thoroughly for the purpose of avoiding a problematic promotion ofpolymer decomposition due to a residual solvent or a problematiceffluxion of a residual solvent upon using a composite electrolyte film.The washing can be accomplished by immersing the porous film in awashing solution. An especially preferred washing solution is water. Thewashing with water is continued preferably until the pH of the wash uponimmersing the porous film in water becomes pH 5 to 8, more preferably6.5 to 7.5.

The steps of extrusion, thin film formation, coagulation, washing anddrying may be conducted continuously or each in a batch mode. It is alsopossible to add between steps other particular steps depending on thepurpose, including impregnation, coating, lamination for making acomposite, orientation, UV or electron beam, corona irradiation for asurface treatment, annealing and the like.

A method in which a porous film made from a polybenzazole obtained by amethod described above is combined with an ion-exchange resin to give acomposite ion-exchange membrane is discussed below. Thus, the porousfilm is immersed in an ion-exchange resin solution without drying toreplace the fluid inside of the porous film with the ion-exchange resinsolution and then dried to obtain a composite ion-exchange membrane.When the fluid inside of the porous film is different from the solventcomposition of the ion-exchange resin solution, the fluid inside may bereplaced previously so that the solvent composition becomes inagreement.

A porous film of the present invention undergoes a shrinkage of the voidstructure in response to the reduction in the volume of the fluid insideof the voids upon drying, resulting characteristically in a substantialreduction in the apparent volume of the film. When the drying iseffected while restricting the shrinkage in the planar direction forexample by means of the fixation to a metal frame without impregnatingthe inside of the porous film with an ion-exchange resin, the shrinkageoccurs in the direction of the film thickness and the apparent filmthickness of the porous film after drying becomes 0.5% to 10% of thefilm thickness before drying.

Due to such characteristics of the porous film, when the porous film isdried after replacing the fluid inside of the voids with an ion-exchangeresin solution, the solvent of the ion-exchange resin solutionimpregnated in the voids evaporates, resulting in a reduction in thevolume of the ion-exchange resin, in response to which the porous filmitself undergoes a shrinkage, which allows a dense composite membranestructure in which the voids inside of the porous membrane is filledwith the precipitated ion-exchange resin to be obtained readily. Such acomposite membrane structure allows an inventive composite ion-exchangemembrane to exhibit an excellent fuel permeation preventing ability. Inthe case of a porous film other than an inventive porous film, forexample a porous film made from an oriented polytetrafluoroethylenepolymer porous membrane, even if the solvent of an ion-exchange resinsolution impregnated in the voids evaporates to reduce the volume of theion-exchange resin solution, the absence of any accompanying shrinkageof the porous film leads to a disadvantage, including the formation of alarge number of voids containing no ion-exchange resin in a resultantdried composite membrane and no formation of the surface layer of theion-exchange resin containing no support on the both side of the porousfilm.

Also in the case of such a composite ion-exchange resin, since a porousfilm undergoes a substantial shrinkage, by adjusting the combination ofthe physical properties of the ion-exchange resin solution such asconcentration, viscosity, solvent volatility and the like with the filmthickness and the void ratio of the porous film, it becomes possible toform a composite layer in which the inside voids of the porous film isfilled with the ion-exchange resin at the same time with allowing anexcessive ion-exchange resin solution depositing on the both sides ofthe porous film or the ion-exchange resin solution exhausted from theinside of the porous film in response to the shrinkage of the film to bedried on the outside surface of the porous film to form a micropore-freeion-exchange resin layer, whereby allowing a structure having surfacelayers of the micropore-free ion-exchange resin on the both side of thecomposite layer as sandwiching the composite layer to be formed readily.

Since a film other than an inventive porous film, such as a porous filmmade from a polytetrafluoroethylene, undergoes no substantial shrinkageas described above, the voids will remain as they are even if theion-exchange resin precipitates inside the porous film upon drying afterimpregnation with the ion-exchange resin solution and it is alsoimpossible to form an ion-exchange resin layer sandwiching the porousfilm composite layer. Although such a condition may somewhat beameliorated by repeating the impregnation of the ion-exchange resin andthe drying several times, the process becomes complicated undesirably.

An ion-exchange resin employed in an inventive composite ion-exchangeresin is not limited particularly, and those which may be employed inaddition to a perfluorocarbonsulfonic acid polymer described above areat least one ionomer of polystyrenesulfonic acid,poly(trifluorostyrene)sulfonic acid, polyvinylphosponic acid,polyvinylcarboxylic acid, polyvinylsulfonic acid polymer, as well as anionomer resulting from sulfonation, phosphonation or carboxylation of atleast one of aromatic polymers such as polysulfone, polyphenylene oxide,polyphenylene sulfoxide, polyphenylene sulfide, polyphenylene sulfidesulfone, polyparaphenylene, polyphenylquinoxaline, polyaryl ketone,polyether ketone, polybenzazole and polyaramid polymer. As used herein,a polysulfone polymer includes at least one of polyethersulfone,polyarylsulfone, polyarylethersulfone, polyphenylsulfone andpolyphenylenesulfone polymers. As used herein, a polyether ketoneincludes at least one of polyetherether ketone, polyether ketone-ketone,polyetherether ketone-ketone and polyether ketone ether-ketone polymers.

A solvent for an ion-exchange resin solution described above may beselected from solvents capable of dissolving the ion-exchange resinwithout dissolving, decomposing or extremely swelling a polybenzazoleporous film. Nevertheless, since the ion-exchange resin is precipitatedby removing the solvent after impregnating the film with theion-exchange resin solution, the solvent is preferably one capable ofbeing removed for example by an evaporation using a means such asheating or reduced pressure. Since an inventive polybenzazole porousfilm here exhibits a high heat resistance, it is possible to form acomposite ion-exchange membrane using an ion-exchange resin solutioncontaining a high boiling solvent which can not be employed in producinga composite ion-exchange membrane using a porous film made from apolytetrafluoroethylene which undergoes a creep at a temperature as lowas 100° C., thus exhibiting an excellent aspect also in view of theselection of a wide range of ion-exchange resins.

While the concentration of an ion-exchange resin solution describedabove or the molecular weight of the ion-exchange resin is not limitedparticularly, they may be selected appropriately depending on the typesof the ion-exchange resin or the film thickness of a compositeion-exchange membrane intended.

A composite ion-exchange membrane thus obtained preferably has anion-exchange resin content of 50% by weight or more. More preferably thecontent is 80% or more. A content below this range is not preferablesince it gives an increased conductive resistance of the membrane and areduced water retaining ability of the membrane, which leads to aninsufficient electricity generating ability.

An inventive ion-exchange membrane is characterized by its surfacelayers consisting of a support-free ion-exchange resin on the both sideof the composite layer as sandwiching the composite layer as describedabove. Since the composite ion-exchange membrane possesses the compositelayer and the surface layers, the composite ion-exchange membrane has ahigh mechanical strength, and is also excellent in terms of the closecontact with an electrode layer when the electrode layer is formed onthe surface. The thickness of each surface layer is 10 μm or more andnot more than 50 μm, and it is preferable that each does not exceed thehalf of the entire thickness of the composite ion-exchange membrane. Athickness of the surface layer below the specified range may affect theclose contact with the electrode layer adversely and leads to aproblematic reduction in the ion conductivity. A thickness of thesurface layer above the specified range results in a difficulty inallowing the reinforcing effect of the composite layer to reach theoutermost surface of the composite ion-exchange membrane, and leads to aproblematic peeling of the surface layer from the composite layer due toa substantial swelling only of the surface layer upon absorption of themoisture by the composite ion-exchange membrane. A further preferablerange of the thickness of the surface layer is 2 μm or more and not morethan 30 μm.

For the purpose of further improving the characteristics such as themechanical strength and the ion conductivity of a composite ion-exchangemembrane and the peeling performance of the ion-exchange resin layerformed on the surface, a method in which the composite ion-exchangemembrane is subjected to a heat treatment under an appropriate conditionis employed preferably. For the purpose of adjusting the thickness ofthe surface layer of the ion-exchange resin formed on the surface, amethod in which the composite ion-exchange membrane is further immersedin the composite ion-exchange resin solution or the compositeion-exchange membrane is coated with the ion-exchange resin solutionprior to the drying whereby increasing the deposition of theion-exchange resin layer, or alternatively, a part of the ion-exchangeresin solution deposited on the porous film surface after immersion inthe ion-exchange resin solution is scraped off using a scraper, airknife, roller and the like or absorbed into a material having a liquidabsorbing ability such as a filter paper or a sponge whereby reducingthe deposition of the ion-exchange resin layer is employed preferably.It is also possible to combine a method for further improving the closecontact with the ion-exchange resin layer using a heat press.

An inventive composite ion-exchange membrane exhibits an excellentmechanical strength while possessing a high ion conductivity. It is alsopossible, by utilizing this aspect, to use as a composite ion-exchangemembrane, especially a polymeric solid electrolyte membrane for a solidpolymeric fuel cell.

An aramid employed in the present invention may for example be apolyparaphenylene terephthalamide or an aramid represented by any ofFormulae 19-1 to 4.

A solvent for forming a solution of such an aramid may for example be apolar solvent such as N,N′-dimethylformamide, N,N′-dimethylacetamide,N-methyl-2-pyrrolidone, γ-butyrolactone and the like. It is alsopossible to use, if necessary, an auxiliary agent such as an amineincluding triethylamine and diethylenetriamine, an alkaline metal saltincluding sodium fluoride, potassium fluoride, cesium fluoride andsodium methoxide. It is also possible to use an acid such as sulfuricacid, polyphosphoric acid, methanesulfonic acid and the like. In thecase of a polyacrylonitrile, a polar solvent described above, an aqueoussolution of sodium thiocyanate or zinc chloride and nitric acid areexemplified.

For a polyamideimide employed in the present invention, an ordinarymethod such as an acid chloride method using trimellitic acid chlorideand diamine and a diisocyanate method employing trimellitic anhydrideand diisocyanate is exemplified. In view of production cost, thediisocyanate method is preferred.

An acid component employed for synthesizing a polyamideimide employed inthe present invention is preferably trimellitic anhydride (chloride), apart of which may be replaced by other polybasic acid or anhydridethereof. For example, a tetracarboxylic acid such as pyromellitic acid,biphenyltetracarboxylic acid, benzophenone tetracarboxylic acid,biphenylether tetracarboxylic acid, ethylene glycol bistrimellitate andpropylene glycol bistrimellitate and an anhydride thereof, an aliphaticdicarboxylic acid such as oxalic acid, adipic acid, malonic acid,sebacic acid, azelaic acid, dodecanedicarboxylic acid,dicarboxypolybutadiene, dicarboxypoly(acrylonitrile-butadiene) anddicarboxypoly(styrene-butadiene), an alicyclic dicarboxylic acid such as1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid,4,4′-dicyclohexylmethanedicarboxylic acid and dimeric acid, an aromaticdicarboxylic acid such as terephthalic acid, isophthalic acid,diphenylsulfone dicarboxylic acid, diphenylether dicarboxylic acid andnaphthalenedicarboxylic acid and the like are exemplified.

It is preferable to copolymerize one or more of butadiene-based rubbers,polyalkylene ethers and polyesters having any of a carboxyl group,hydroxyl group and amino group at the terminal. A butadiene-based rubberis preferably a dicarboxypolybutadiene,dicarboxypoly(acrylonitrile-butadiene),dicarboxypoly(styrene-butadiene), diaminopolybutadiene,diaminopoly(acrylonitrile-butadiene) or diaminopoly(styrene-butadiene)whose molecular weight is 1000 or more.

By replacing a part of a trimellitic acid compound with a glycol, apolyalkylene ether or polyester copolymer can be obtained. A glycol mayfor example be an alkylene glycol such as ethylene glycol, propyleneglycol, tetramethylene glycol, neopentyl glycol and hexanediol, apolyalkylene glycol such as polyethylene glycol, polypropylene glycoland polytetramethylene glycol, as well as a polyester having terminalhydroxyl groups synthesized from one or more of the dicarboxylic acidsdescribed above together with one or more of the glycols describedabove. It is preferable to copolymerize a polyethylene glycol whosemolecular weight is 1000 or more or a polyester having terminal hydroxylgroups. The amount of such a copolymerization is preferably 2 to 30% bymole based on 100% by mole of the entire acid component. Thecopolymerization described above serves to enhance the toughness of aporous sheet.

A diamine (diisocyanate) component employed for synthesizing apolyamideimide may for example be an aliphatic diamine such as ethylenediamine, propylene diamine and hexamethylene diamine and a diisocyanatethereof, an alicyclic diamine such as 1,4-cyclohexane diamine,1,3-cyclohexane diamine, isophorone diamine and 4,4′-dicyclohexylmethanediamine and a diisocyanate thereof, an aromatic diamine such asm-phenylene diamine, p-phenylene diamine, 4,4′-diaminodiphenylmethane,4,4′-diaminodiphenyl ether, 4,4′-diaminodiphenyl sulfone, benzidine,o-tolidine, 2,4-tolylene diamine, 2,6-tolylene diamine and xylylenediamine and a diisocyanate thereof and the like, with4,4′-diaminodiphenylmethane, o-tolidine diamine and isocyanates thereofbeing preferred in view of reactivity, cost and chemical resistance. Itis further preferable to copolymerize o-tolidine and diisocyanatethereof. The amount of such a copolymerization is preferably 30 to 80%by mole based on 100% by mole of the entire amine component. Thiscopolymerization serves to enhance the strength of a porous sheet.

A polyamideimide described above preferably has a logarithmic viscosityof 0.5 dl/g or higher and a glass transition temperature of 100° C. orhigher in view of the heat resistance and the strength.

A solvent capable of dissolving a polyamideimide employed in the presentinvention is not limited as long as it has such a function, and may forexample be a polar solvent such as N,N′-dimethylformamide,N,N′-dimethylacetamide, N-methyl-2-pyrrolidone and γ-butyrolactone. Ifnecessary, an auxiliary agent may be employed including an amine such astriethylamine and diethylene triamine and an alkaline metal salt such assodium fluoride, potassium fluoride, cesium fluoride and sodiummethoxide.

A solution in a solvent described above may be obtained by dissolving apolyamideimide in a solvent described above, or a solution obtained by apolymerization may directly be employed when the polyamideimide waspolymerized by a solution method. In such a method, incorporation of anadditive such as a pore size adjusting agent during or afterpolymerization, or adjustment of the polymer concentration may becarried out.

An aramid film and a polyamideimide film can be obtained using asolution described above by a film forming method similar to that for apolybenzazole solution, via a procedure in which a thin film made by aroll, slit or press from a polymer solution sandwiched between twosupports is introduced into a coagulating bath and the supports arepeeled off in the coagulating bath to effect the coagulation.

BEST MODES FOR CARRYING OUT THE INVENTION

The present invention is described further typically based on Examplesshown below. Nevertheless, the present invention is not restricted bythese Examples.

The methods for measurement and evaluation employed in Examples aredescribed below.

(Evaluation Methods, Measurement Methods)

1. Polybenzazole Film Structure Observation (by TEM)

A transmission electron microscope (TEM) was used to observe thesectional structure of a membrane in accordance with the followingprocedure.

First, a observation test piece was produced as described below. Thus,the water inside of a porous film sample after washing with water wasreplaced with ethanol, and then also replaced with an epoxy monomersufficiently. The sample was allowed to stand for 6 hours at 45° C. inthe epoxy monomer, and then subjected to a heat treatment for 20 hoursat 60° C. whereby setting the epoxy (epoxy embedding). The sample thusembedded with the epoxy was cut by a microtome fitted with a diamondknife into a super-thin section having a thickness allowing theinterference color to be silver to gold, which was then treated with aKOH-saturated ethanol solution for 15 minutes to remove the epoxy (epoxyremoval). Then the sample was washed with ethanol followed by water,stained with RuO₄ and then subjected to a carbon vapor deposition, andthen observed at an acceleration voltage of 200 kV using a TEMmanufactured by JEOL Ltd. (JEM-2010).

2. Polybenzazole Film Structure Observation (by AFM)

The structure was observed using an atomic force microscope (AFM) inaccordance with the following procedure. Thus, an AFM manufactured bySeiko Instruments Inc. (SPA 300, observation mode: DFM mode, Sensorlever: SI-DF3, Scanner: FS-100A) was used to observe the surfacestructure of a porous film which was not dried but retained on thesample stage in water.

3. Polybenzazole Limiting Viscosity

The viscosity of a polymer solution prepared at a concentration of 0.5g/l using methanesulfonic acid as a solvent was measured in a 25° C.thermostat chamber using an Ubbelohde viscometer and calculated.

4. Polybenzazole Film Thickness

The thickness of a porous film which was not dried was measured by amethod described below. Using a micrometer whose measurable load wasvariable, the thickness of a film in water under each load was measured.The measured thickness was plotted verses the load, and the value of theintercept when extrapolating the linear part to load 0 was assumed asthe thickness, and the average of the thicknesses measured at 5positions per sample was designated as the film thickness.

5. Composite Ion-Exchange Membrane Thickness and Thickness of LayerConstituting the Same

For measuring the thicknesses of a composite layer constituting thecomposite ion-exchange membrane and the surface layer consisting of anion-exchange resin excluding a porous film formed on the both side of acomposite layer with sandwiching the composite layer, a compositemembrane piece cut out as a porous film in a size of 300 μm width and 5mm length was embedded in a resin whose composition was LUVEAC 812 (madeby Nacalai Tesque Inc.)/LUVEAC NMA (made by Nacalai Tesque Inc.)/DMP 30(TAAB)=100/89/4, and cured for 12 hours at 60° C. to obtain a sampleblock. Using an ultra-microtome (2088 ULTROTOME® V manufactured by LKBCo., Ltd.), the tip of the block was shaved using a diamond knife(SK2045 made by Sumitomo Electric Industries, Ltd.) so that a smoothsection was exposed. The section of the composite membrane thus exposedwas photographed using an optical microscope, and measurement was on thebasis of the comparison with a scale having a known length photographedat the same magnification. While there may be a case where the voidratio of the porous membrane support and where there was no clearinterface between at least one surface layer and the composite layerinside thereof and the structure near the interface is alteredcontinuously, such a case is subjected to a procedure in which a partclosest to the outer surface of the composite ion-exchange membraneamong the parts where a continuous structural alteration can beidentified by the optical microscope is regarded as the outermostsurface of the composite layer, the distance from which to the outersurface of the composite ion-exchange membrane is regarded as thethickness of the surface layer.

6. Ion Exchange Resin (ICP) Content of Composite Ion-Exchange Membrane

The ion-exchange resin content of a composite ion-exchange membrane wasmeasured by a method described below. The unit weight Dc [g/m²] of acomposite ion-exchange membrane dried under vacuum for 6 hours at 11° C.was measured, and the unit weight Ds (g/m²) of a porous film measuredafter drying a porous film produced under the condition similar to thatemployed for producing the composite ion-exchange membrane which thistime was not combined with the ion-exchange resin was also used tocalculate the ion-exchange resin content in accordance with thefollowing equation.Ion exchange resin content (% by weight)=(Dc−Ds)/Dc×100

The ion-exchange resin content of the composite ion-exchange membranecan be measured also by a method described below. Thus, the compositeion-exchange membrane was immersed in a solvent capable of dissolvingeither one of the porous film component or the ion-exchange resincomponent in the composite ion-exchange membrane to extract either onecomponent off, and the change in the weight when compared with theinitial composite ion-exchange membrane was measured to obtain theion-exchange resin content.

7. Ion Exchange Resin Strength and Tensile Elasticity

The strength of an ion-exchange resin was measured using a “Tensilon”manufactured by “Orientec Co. Ltd.” in atmosphere of 25° C. and 50%relative humidity. A sample as a strip whose width was 10 mm wasmeasured with a chuck distance of 40 mm and a tensile speed of 20 mm/secto obtain a stress strain curve, which was then used in the calculation.

8. Ion Conductivity of Ion-Exchange Membrane

The ion conductivity σ was measured as described below. On alaboratory-made measurement probe (made from tetrafluoroethylene),platinum wires (diameter: 0.2 mm) were pressed against the surfaces of astrip membrane sample whose width was 10 mm, and the sample was retainedin a 95% RH chamber at constant temperature and humidity, and thealternating impedance at 10 kHz between the platinum wires was measuredusing 1250 FREQUENCY RESPONSE ANALYZER manufactured by SOLARTRON, Themeasurement was conducted while changing the inter-electrode distancefrom 10 mm to 40 mm by a 10 mm interval, and the slope Dr [Ω/cm] of theline obtained by plotting the inter-electrode distance versus themeasured resistance was used in the calculation in accordance with thefollowing equation while canceling the contact resistance between themembrane and the platinum wire.σ (S/cm)=1/(membrane width×membrane thickness (cm)×Dr)9. Gas Permeability of Ion-Exchange Membrane

The gas permeability of an ion-exchange membrane was measured by thefollowing method. An ion-exchange membrane was placed on a meshstainless steel support, immobilized to a holder, and then one side ofthe ion-exchange membrane was exposed to the flow of a helium gassaturated with water vapor at room temperature under a gauge pressure of0.09 MPa, and the amount of the helium gas permeate to the other side ofthe ion-exchange membrane was determined by a soap membrane orifice.

10. Electricity Generation Property of Ion-Exchange Membrane

A 20% solution of “Nafion®” (trade name) manufactured by DuPont (productcode: SE-20192) was combined with a platinum-loaded carbon (Carbon:Valcan XC-72 manufacture by Cabot, platinum load: 40% by weight) so thatthe weight ratio of the platinum and “Nafion®” became 2.7:1, and stirredto obtain a catalyst paste. This catalyst paste was coated onto a Toraycarbon paper TGPH-050 so that the platinum deposition became 1 mg/cm²,and then dried to obtain an electrode catalyst layer-carrying gasdiffusion layer. Between two electrode catalyst layer-carrying gasdiffusion layers, a membrane sample was sandwiched so that the electrodecatalyst layer was brought into contact with the membrane sample, andheated under pressure for 3 minutes at 120° C. and 2 MPa by a hot pressmethod to obtain a membrane-electrode assembly. This assembly wasintegrated into a fuel cell for laboratory assessment manufactured byElectrochem, namely, CELL FC25-02SP, and examined for the electricitygenerating property at a cell temperature of 80° C., gas moisturizingtemperature of 80° C., at flow rates of 300 ml/min for hydrogen as afuel gas and 1000 ml/min for air as an oxidizing gas.

11. Physical Properties of Dried Polybenzazole Film

(Surface Roughness)

A film after drying was examined for a square mean roughness using atri-dimensional non-contact surface shape measurement system “Micromap”manufactured by Ryoka Systems Inc.

12. Tensile Elasticity of Polybenzazole Film

A film after drying was cut in a longitudinal direction (MD direction)or widthwise direction (TD direction) into a strip of 100 mm in lengthand 10 mm in width, which was subjected to a tensile test with a tensilespeed of 50 mm/sec and a chuck distance of 40 mm using a tensilemeasurement device (Shimadzu Corp. Autograph, model AG-5000A) todetermine the tensile elasticity.

13. Temperature Dependency of Elasticity and % Elasticity Keeping ofPolybenzazole Film

A film after drying was cut in a longitudinal direction (MD direction)or widthwise direction (TD direction) into a strip of 40 mm in lengthand 5 mm in width which was subjected to a measurement at a temperatureranging from room temperature to 400° C. at an elevation speed of 5°C./min and also at 10 Hz using a dynamic viscosity meter (manufacturedby IT KEISOKU SEIGYO Inc. model DVA-225). As an elasticity keepingratio, the elasticity ratio of 300° C./30° C. was employed.

14. Interlaminar Peeling Test of Polybenzazole Film

A film after drying was cut in a longitudinal direction (MD direction)or widthwise direction (TD direction) into a strip of 20 mm in lengthand 10 mm in width, and the both sides of the film were stuck to theadhesion surfaces of adhesive tapes.

The tape was peeled slowly with a tensile speed of 50 mm/sec and a chuckdistance of 40 mm using a tensile measurement device (Shimadzu Corp.,Autograph®, model AG-5000A) to examine whether there was anyinterlaminar peeling phenomenon which was observed as a migration of thefilm onto the adhesion surfaces of the both adhesive tapes (see FIG. 2).

15. Observation of Aramid Film and Polyamide Film Surface Micropore

Using a scanning electron microscope (manufactured by Hitachi, Ltd.Model S800) at a magnification of 5000, the presence of micropores wasinvestigated.

16. Thickness Accuracy (Change Ratio in Thickness) of Aramid Film andPolyamideimide Film

The thickness was measured using a micrometer (manufactured by FeinprüfGMBH, “Millitron 1245D”). The thickness unevenness was designated as a %obtained by measuring the film thickness of a resultant 20 mm×100 mmfilm at 10 positions and dividing the difference between the maximumthickness and the minimum thickness by the mean thickness.

17. Uniformity of Both Sides of Aramid Film and Polyamideimide Film

The surfaces on the both sides of a film were evaluated visually andjudged as poor when the surface gloss or roughness was clearly differentbetween the both sides, and judged as good when there was no cleardifference between the both sides.

18. Logarithmic Viscosity of Polyamideimide

A solution obtained by dissolving 0.5 g of a polyamideimide in 100 ml ofN-methyl-2-pyrrolidone was kept at 30° C. and subjected to themeasurement using an Ubbelohde viscometer.

19. Glass Transition Temperature of Polyamideimide Film

A polyamideimide-based film having the measurement size of 4 mm widthand 15 mm length was subjected to the measurement using a “RheospectraDVE-V4” manufactured by Rheology Co., Ltd. with a vibration at 110 Hz toobtain a loss elasticity of the dynamic viscoelasticity, the inflectionpoint of which was regarded as a glass transition temperature.

EXAMPLE A1

A solution containing 14% by weight of a polyphenylenecisbenzobisoxazole polymer of IV=24 dl/g in polyphosphoric acid wasdiluted with methanesulfonic acid to form an isotropic solution whosepolyparaphenylene cisbenzobisoxazole concentration was 2.5% by weight.This solution was passed through a filter purported to have a pore sizeof 20 μm, and then sandwiched between two porous supports made from apolypropylene provided between two counter rolls, which were thenrotated in opposite directions to roll the solution while feeding thesolution together with the polypropylene porous supports, and thencoagulated for 30 minutes in atmosphere of the chamber kept constantlyat 25° C. and 80% relative humidity, and then introduced into acoagulation bath. The coagulation solution was water at 60° C. Duringthe step described above, the gap between the counter rolls was adjustedso that the solution thickness became 200 μm. In the coagulation bath,the polypropylene porous supports were peeled off and the solution wasbrought into contact with the coagulation solution to effect a furthercoagulation. A schematic view of the production method is shown inFIG. 1. Thereafter, the produced film was washed with water until thewash exhibited pH 7±0.5, whereby obtaining a porous film made from thepolybenzazole. The resultant polybenzazole porous film was proven to bea porous film having continuous pores whose openings were present on theboth sides, as evident from a surface morphology observation using anatomic force microscope and a sectional morphology observation using atransmission electron microscope. For a dried membrane, the coagulatedfilm after washing with water obtained as described above was subjectedto a heat fixation for 20 seconds at 150° C. while the both ends wereheld by a tenter, whereby obtaining a polybenzazole film whose thicknesswas 5.2 μm. The film after drying was examined for a square meanroughness using a tri-dimensional non-contact surface shape measurementsystem “Micromap” manufactured by Ryoka Systems Inc. The results of themeasurements of the interlaminar peeling, tensile elasticity anddependency of elasticity on temperature are shown in Table 2.

COMPARATIVE EXAMPLE A1

A solution containing 14% by weight of a polyparaphenylenecisbenzobisoxazole polymer of IV=24 dl/g in polyphosphoric acid wasdiluted with methanesulfonic acid to form an isotropic solution whosepolyparaphenylene cisbenzobisoxazole concentration was 2.5% by weight.This solution was subjected to a film forming process at a film formingspeed of 5 mm/second using an applicator whose clearance was 300 μm on aglass plate heated at 70° C. Since under this condition thepolybenzazole solution became highly viscose and streaks were formed inthe direction of a squeegee, it was impossible to obtain a smooth film.The solution film formed on the glass plate as described above wascoagulated by placing in a chamber kept constantly at 25° C. and 80%relative humidity, and the resultant film, and the resultant film waswashed with water until the wash exhibited pH7±0.5, whereby obtaining aporous film made from the polybenzazole. The resultant porous film had adense structure of the surface on the side in contact with the supportbut had a porous structure on the surface on the side not in contactwith the support, as evident from a surface morphology observation usingan atomic force microscope and a sectional morphology observation usinga transmission electron microscope, whereby proving that it was amembrane which did not have the openings on the both sides.

COMPARATIVE EXAMPLE A2

A solution containing 14% by weight of a polyparaphenylenecisbenzobisoxazole polymer of IV=24 dl/g in polyphosphoric acid wasdiluted with methanesulfonic acid to form an isotropic solution whosepolyparaphenylene cisbenzobisoxazole concentration was 2.5% by weight.This solution was passed through a filter purported to have a pore sizeof 20 μm, and then sandwiched between two supports made from apolyethylene terephthalate film provided between two counter rolls,which were then rotated in opposite directions to roll the solutionwhile feeding the solution together with the polyethylene terephthalatefilm supports, and then introduced into a coagulation bath. Thecoagulation solution was water at 60° C. During the step describedabove, the gap between the counter rolls was adjusted so that thesolution thickness became 200 μm. In the coagulation bath, thepolyethylene terephthalate film supports were peeled off and thesolution was brought into contact with the coagulation solution toeffect a further coagulation. Thereafter, the produced film was washedwith water until the wash exhibited pH 7±0.5, whereby obtaining a porousfilm made from the polybenzazole. The resultant polybenzazole porousfilm was proven to be a film having no openings on the both sides, asevident from a surface morphology observation using an atomic forcemicroscope and a sectional morphology observation using a transmissionelectron microscope. For a dried membrane, the coagulated film afterwashing with water obtained as described above was subjected to a heatfixation for 20 seconds at 150° C. while the both ends were held by atenter, whereby obtaining a polybenzazole film whose thickness was 5.4μm. The film after drying was examined for a square mean roughness usinga tri-dimensional non-contact surface shape measurement system“Micromap” manufactured by Ryoka Systems Inc. The results of themeasurements of the interlaminar peeling, tensile elasticity anddependency of elasticity on temperature are shown in Table A1. TABLE A1Comparative Example Example A1 A2 Film forming method Counter rollsCounter rolls PET film support Porous polypropylene film support Surfaceroughness 0.08 0.30 (μm) Interlaminar peeling Absent/AbsentAbsent/Present MD/TD Tensile elasticity 980/950 580/540 MD/TD (kg/mm²)Elasticity retention MD direction (%) 300° C./30° C. 82 80 400° C./30°C. 75 72

From Comparative Example A1, it was impossible to obtain a smooth filmby the production method employing the rolling, since the polybenzazolesolution became highly viscose and allowed the streaks to be formed inthe direction of the squeegee. In addition, the surface on the side incontact with the support underwent the formation of a dense structure.On the other hand, by the production method according to the presentinvention which is Example A1, a smooth film can be obtained even if thepolybenzazole becomes highly viscose and a porous membrane havingcontinuous pores whose openings are present on the both surfaces can beproduced. When Comparative Example A2 is carried out using the supportsthrough which a poor solvent such as the polybenzazole or a vaporthereof could not permeate to effect the molding followed immediately byintroduction into the coagulation bath containing the coagulationsolution which is a poor solvent having a strong coagulating abilitywhere the supports are peeled to effect the direct contact with thecoagulation solution whereby accomplishing the coagulation, the surfacestructure of the membrane becomes dense and does not allow the porousstructure to be formed.

EXAMPLE A2

A solution containing 14% by weight of a polyparaphenylenecisbenzobisoxazole polymer of IV=24 dl/g in polyphosphoric acid wasdiluted with methanesulfonic acid to form an isotropic solution whosepolyparaphenylene cisbenzobisoxazole concentration was 2.5% by weight.This solution was passed through a filter purported to have a pore sizeof 20 μm, and then sandwiched between two porous film supports made froma polypropylene provided between two counter rolls, which were thenrotated in opposite directions to roll the solution while feeding thesolution together with the polypropylene porous supports, and thencoagulated for 30 minutes in atmosphere of the chamber kept constantlyat 25° C. and 80% relative humidity, and then introduced into acoagulation bath. The coagulation solution was water at 60° C. Duringthe step described above, the gap between the counter rolls was adjustedso that the solution thickness became 200 μm. In the coagulation bath,the polypropylene porous supports were peeled off and the solution wasbrought into contact with the coagulation solution to effect a furthercoagulation. Thereafter, the produced film was washed with water untilthe wash exhibited pH7±0 5, whereby obtaining a porous film made fromthe polybenzazole. This porous film was fixed to a stainless steel framein water and the water inside of the porous film was replaced with asolvent mixture of water ethanol:1-propanol=26:26:48 (weight ratio)which was almost similar to the solvent composition of a 20% solution of“Nafion®” (trade name) manufactured by DuPont (product code: SE-20192)which was an ion-exchange resin solution. This porous film was immersedfor 15 hours at 25° C. in a 20% solution of “Nafion®” (trade name) andthen taken out, and the solvent for the “Nafion®” (trade name) solutionimpregnating the inside of the membrane and depositing on the surfacesof the membrane was evaporated in the air whereby being dried. The driedfilm was subjected to a preliminary heat treatment for 1 hour in an ovenat 60° C. to remove any residual solvent, followed by a heat treatmentfor 1 hour at 150° C. in a nitrogen atmosphere to produce a compositeion-exchange membrane of Example A2.

COMPARATIVE EXAMPLE A3

As Comparative Example A3, a commercially available “Nafion®” 112 (tradename) manufactured by DuPont was employed. This film is a protonexchange membrane made from a perfluorocarbon sulfonic acid polymersimilarly to the “Nafion®” polymer contained in a 20% solution of“Nafion®” employed in Example A1 and a 10% solution of “Nafion®”employed in Example A2, and employed widely as a proton exchangemembrane for a solid polymeric fuel cell.

COMPARATIVE EXAMPLE A4

A solution containing 14% by weight of a polyparaphenylenecisbenzobisoxazole polymer of IV=24 dl/g in polyphosphoric acid wasdiluted with methanesulfonic acid to form an optically anisotropicsolution whose polyparaphenylene cisbenzobisoxazole concentration was 8%by weight. This solution was passed through a filter purported to have apore size of 20 μm, and then sandwiched between two porous supports madefrom a polypropylene provided between two counter rolls, which were thenrotated in opposite directions to roll the solution while feeding thesolution together with the polypropylene porous supports, and thencoagulated for 30 minutes in atmosphere of the chamber kept constantlyat 25° C. and 80% relative humidity, and then introduced into acoagulation bath. The coagulation solution was water at 60° C. Duringthe step described above, the gap between the counter rolls was adjustedso that the solution thickness became 200 μm. In the coagulation bath,the polypropylene porous supports were peeled off and the solution wasbrought into contact with the coagulation solution to effect a furthercoagulation. Thereafter, the produced film was washed with water untilthe wash exhibited pH7±0.5, whereby obtaining a porous film. This filmwas fixed to a stainless steel frame in water and the water inside ofthe porous film was replaced with a solvent mixture ofwater:ethanol:1-propanol=26:26:48 (weight ratio) which was almostsimilar to the solvent composition of a 20% solution of “Nafion®” (tradename) manufactured by DuPont (product code: SE-20192) which was anion-exchange resin solution. This porous film was immersed for 15 hoursat 25° C. in a 20% solution of “Nafion®” (trade name) and then takenout, and the solvent for the “Nafion®” (trade name) solutionimpregnating the inside of the membrane and depositing on the surfacesof the membrane was evaporated in the air whereby being dried. The driedfilm was subjected to a preliminary heat treatment for 1 hour in an ovenat 60° C. to remove any residual solvent, followed by a heat treatmentfor 1 hour at 150° C. in a nitrogen atmosphere to produce a compositeion-exchange membrane of Comparative Example A4.

COMPARATIVE EXAMPLE A5

A solution containing 14% by weight of a polyparaphenylenecisbenzobisoxazole polymer of IV=24 dl/g in polyphosphoric acid wasdiluted with methanesulfonic acid to form an isotropic solution whosepolyparaphenylene cisbenzobisoxazole concentration was 2.5% by weight.This solution was subjected to a film forming process at a film formingspeed of 5 mm/second using an applicator whose clearance was 300 μm on aglass plate heated at 70° C. Since under this condition thepolybenzazole solution became highly viscose and streaks were formed inthe direction of a squeegee, it was impossible to obtain a smooth film.The solution film formed on the glass plate as described above wascoagulated by placing in a chamber kept constantly at 25° C. and 80%relative humidity, and the resultant film, and the resultant film waswashed with water until the wash exhibited pH 7±0.5, whereby obtaining aporous film. This film was fixed to a stainless steel frame in water andthe water inside of the porous film was replaced with a solvent mixtureof water:ethanol:1-propanol=26:26:48 (weight ratio) which was almostsimilar to the solvent composition of a 20% solution of “Nafion®” (tradename) manufactured by DuPont (product code: SE-20192) which was anion-exchange resin solution. This porous film was immersed for 15 hoursat 25° C. in a 20% solution of “Nafion®” (trade name) and then takenout, and the solvent for the “Nafion® ” (trade name) solutionimpregnating the inside of the membrane and depositing on the surfacesof the membrane was evaporated in the air whereby being dried. The driedfilm was subjected to a preliminary heat treatment for 1 hour in an ovenat 60° C. to remove any residual solvent, followed by a heat treatmentfor 1 hour at 150° C. in a nitrogen atmosphere to produce a compositeion-exchange membrane of Comparative Example A5.

The physical parameters of Example A2, Comparative Examples A3, A4 andA5 are shown in Table A2. TABLE A2 Compar- Compar- Compar- ative ativeative Example Example Example Example A2 A3 A4 A5 Entire μm 50 49 48 53thickness composite ion-exchange membrane Thickness of μm 17 15 18Surface layer B Thickness of μm 19 21 20 Composite layer ICP wt % 95 10046 39 content Ion S/cm 0.19 0.20 0.04 0.01 conductivity Break MPa 27 22144 13 strength Tensile MPa 863 317 2825 824 elasticity Gas cm³ · cm/1.6 × 10⁻⁶ 3.6 × 10⁻⁶ 1.5 × 10⁻⁶ 1.2 × 10⁻⁶ permeability cm² · s · MPaPower- A/cm² (at 0.7 0.8 0.2 0.1 generating 0.2 V) performance

The composite ion-exchange membrane of Example 2A was proven to be anion-exchange membrane having higher break strength and tensileelasticity when compared with the commercially available “Nafion®” 112membrane which was Comparative Example A3. It was also proven that thecomposite ion-exchange membrane of Example 2A possessed excellentcharacteristics required in a polymeric solid electrolyte membrane for afuel cell since its gas permeability was kept at a level less than thehalf of the value of the porous support-free Comparative Example A3without undergoing a substantial reduction in the ion conductivity orthe electricity generating performance in spite that it contained poroussupports inside of it. When using a film made from the polybenzazoleobtained from an optically anisotropic solution of Comparative ExampleA4, the both of the ion conductivity and the electricity generatingperformance were reduced, and it was impossible to obtain excellentcharacteristics required in a polymeric solid electrolyte membrane for afuel cell. The composite ion-exchange membrane employing the porous filmmade by the rolling method of Comparative Example A5 had a problematicdifficulty in obtaining a smooth membrane (film) and underwent areduction both in the ion conductivity and the electricity generatingperformance, thus being impossible to possess excellent characteristicsrequired in a polymeric solid electrolyte membrane for a fuel cell.

EXAMPLE B1

A 3% by weight solution of a polyparaphenylene terephthalamide resinwhose logarithmic viscosity was 6 in 100% sulfuric acid was passedthrough a filter purported to have a pore size of 20 μm, and thensandwiched between two porous supports made from a polypropyleneprovided between two counter rolls, which were then rotated in oppositedirections to roll a dope while feeding together with the polypropyleneporous supports, and then introduced into a coagulation bath. Thecoagulation solution was 30% sulfuric acid at 25° C. During the stepdescribed above, the gap between the counter rolls was adjusted so thatthe solution thickness became constant. In the coagulation bath, thepolypropylene porous supports were peeled off and the resin solutionthin later was brought into contact with the coagulation solution toeffect a further coagulation. A schematic view of the production methodis shown in FIG. 1. Thereafter, the resin film thus formed was washedwith warm water at 50° C., then dried at 130° C. under tension, wherebyobtaining an aramid film whose thickness was 25 μm. The results of theevaluation of the resultant film are shown in Table B1.

COMPARATIVE EXAMPLE B1

An aramid film of Comparative Example B1 was obtained similarly toExample B1 except for employing an alternative procedure in which aresin solution whose polyparaphenylene terephthalic amide concentrationwas 15% by weight was extruded via a die onto a biaxially orientedpolyester film whose thickness was 100 μm to form a thin layer of thearamid solution which was then brought into contact with a coagulationsolution. The results of the evaluation of the resultant film are shownin Table B1.

EXAMPLE B2

An aramid film of Example B2 was obtained similarly to Example B1 exceptfor employing an alternative procedure in which the aramid compositionwas changed to a copolymer whose 20% by mole of the diamine componenthad been replaced with 4,4-diaminodiphenylsulfone, the solvent waschanged to dimethylformamide, the aramid concentration was 10% by weightand a composite laminate sandwiched between two biaxially orientedpolyester film supports was brought into contact with a coagulationsolution. The results of the evaluation of the resultant film are shownin Table B1.

EXAMPLE B3

An aramid film of Example B3 was obtained similarly to Example B1 exceptfor employing an alternative procedure in which the aramid compositionwas changed to a copolymer whose 20% by mole of the diamine componenthad been replaced with 4,4-diaminodiphenylsulfone, the solvent waschanged to dimethylformamide, and a composite laminate sandwichedbetween two porous supports was subjected to a preliminary coagulationin an atmosphere kept constant at 50° C. and 90% RH before being broughtinto contact with a coagulation solution which was water. The results ofthe evaluation of the resultant film are shown in Table B1.

The aramid films of Examples B1 to B3 were excellent in terms of thethickness accuracy and the uniformity in the structure between the bothsides of the film, thus being highly suitable to a practical use. Inaddition, the respective production methods involved simple deviceswhich gives an economical advantage. On the other hand, the aramid filmobtained in Comparative Example B1 had a poor thickness accuracy and apoor uniformity in the structure between the both sides of the film,thus being poorly suitable to a practical use. In addition, it was pooralso from an economical point of view unlike to Example B1 because itneeded an extruder and a die for extruding the aramid solution whichraised the cost of equipments. TABLE B1 Film thickness accuracyThickness Film surface Uniformity between variation (%) structure bothsides of film Example B1 5.2 Porous Good Example B2 4.9 Non-porous GoodExample B3 5.2 Porous Good Comparative 10.5 Porous Poor Example B1

EXAMPLE C1

A four-necked flask fitted with a thermometer, condenser and nitrogengas inlet was charged with 1 mole of trimellitic anhydride (TMA), 1 moleof diphenylmethane diisocyanate (MDI) and 0.01 mole of potassiumfluoride together with N-methyl-2-pyrrolidone at a solid concentrationof 20% by weight, stirred for 1.5 hours at 120° C., and then heated upto 180° C. at which the stirring was continued for about 3 hours wherebysynthesizing a polyamideimide. The resultant polyamideimide had alogarithmic viscosity of 0.86 dl/g and a glass transition temperature of290° C.

The polyamideimide solution described above was passed through a filterpurported to have a pore size of 20 μm, and then sandwiched between twoporous supports made from a polypropylene provided between two counterrolls, which were then rotated in opposite directions to roll a dopewhile feeding together with the polypropylene porous supports, and thenintroduced into a coagulation bath. The coagulation solution waswater/isopropanol (volume ratio: 4/1) at 25° C. During the stepdescribed above, the gap between the counter rolls was adjusted so thatthe polymer solution thickness became constant. In the coagulation bath,the polypropylene porous supports were peeled off and the polyamideimidesolution in the form of a film was brought into contact with thecoagulation solution to effect a further coagulation. A schematic viewof the production method is shown in FIG. 1. Thereafter, the film thusformed was dried at 130° C. under tension, whereby obtaining apolyamideimide film whose thickness was 25 μm. The results of theevaluation of the resultant film are shown in Table C1.

COMPARATIVE EXAMPLE C1

A polyamideimide film of Comparative Example C1 was obtained similarlyto Example C1 except for employing an alternative procedure in which thepolyamideimide solution was extruded via a die onto a biaxially orientedpolyester film whose thickness was 100 μm to form the polyamideimidesolution in the form of a film which was then brought into contact witha coagulation solution. The results of the evaluation of the resultantfilm are shown in Table C1.

EXAMPLE C2

A polyamideimide film of Example C2 was obtained similarly to Example C1except for using 0.9 mole of TMA and 0.1 mole ofdicarboxypoly(acrylonitrile-butadiene) rubber (UBE INDUSTRIES LTD.,“Hycar” CTBN1300×13: molecular weight: 3500) as acid components. Theresults of the evaluation of the resultant film are shown in Table C1.The polyamideimide obtained in this Example had a logarithmic viscosityof 0.65 dl/g and a glass transition temperature of 203° C. The resultsof the evaluation of the resultant film are shown in Table C1.

EXAMPLE C3

Using the devices employed in Example C1, 0.94 mole of TMA, 0.06 mole ofpolyproplyene glycol whose molecular weight was 2000 and 1.02 mole ofisophorone diisocyanate were charged together with γ-butyrolacton at asolid concentration of 50% by weight, reacted for 3 hours at 200° C.,and then diluted with N-methyl-2-pyrrolidone so that the solidconcentration became 20% by weight whereby synthesizing a polyamideimidesolution. The resultant polyamideimide had a logarithmic viscosity of0.63 dl/g and a glass transition temperature of 198° C. A polyamideimidefilm of Example C3 was obtained similarly to Example C1 using thepolyamideimide solution obtained as described above. The results of theevaluation of the resultant film are shown in Table C1.

EXAMPLE C4

Using the devices employed in Example C1, 0.93 mole of TMA, 0.07 mole ofpolycaprolacton (PLACCEL 220 made by Daicel Chemical Industries, Ltd.,molecular weight: 2000), 1.02 mole of MDI and 0.02 mole of potassiumfluoride were charged together with γ-butyrolacton at a solidconcentration of 20% by weight, reacted for 5 hours at 200° C., and thendiluted with N-methyl-2-pyrrolidone so that the solid concentrationbecame 20% by weight whereby synthesizing a polyamideimide solution. Theresultant polyamideimide had a logarithmic viscosity of 0.71 dl/g and aglass transition temperature of 175° C. A polyamideimide film of ExampleC4 was obtained similarly to Example C1 using the polyamideimidesolution obtained as described above. The results of the evaluation ofthe resultant film are shown in Table C1.

EXAMPLE C5

Using the devices employed in Example C1, 0.5 mole of TMA, 0.5 mole of adimeric acid, 0.5 mole of o-tolidine diisocyanate and 0.5 mole of MDIwere charged together with N-methyl-2-pyrrolidone at a solidconcentration of 30% by weight, reacted for 5 hours at 120° C. and then3 hours at 180° C., and then diluted with N-methyl-2-pyrrolidone so thatthe solid concentration became 20% by weight whereby synthesizing apolyamideimide solution. The resultant polyamideimide had a logarithmicviscosity of 0.70 dl/g and a glass transition temperature of 153° C.Using the polyamideimide solution obtained as described above, apolyamideimide film of Example C5 was obtained similarly to Example C1except for using water/isopropanol (2/1 volume ratio) as a coagulationsolution. The results of the evaluation of the resultant film are shownin Table C1.

EXAMPLE C6

A polyamideimide film of Example C6 was obtained similarly to Example C1except that the solid concentration of the polyamideimide solution was28% by weight and the two supports were non-porous PET films. Theresults of the evaluation of the resultant film are shown in Table C1.

The polyamideimide films of Examples C1 to C6 were excellent in terms ofthe thickness accuracy and the uniformity in the structure between theboth sides of the film, thus being highly suitable to a practical use.In addition, the respective production methods involved simple deviceswhich gives an economical advantage. On the other hand, thepolyamideimide film obtained in Comparative Example C1 had a poorthickness accuracy and a poor uniformity in the structure between theboth sides of the film, thus being poorly suitable to a practical use.In addition, it was poor also from an economical point of view unlike toExample C1 because it needed an extruder and a die for extruding thepolyamideimide solution which raised the cost of equipments. Eachpolyamideimide film of Examples C1 to C5 was porous and can be employedpreferably as an impregnation film such as a separation membrane such asa separator in a cell or an electrolyte retaining membrane in a cell. Onthe other hand, the polyamideimide film of Example C6 was non-porous andcan be employed preferably as a substrate film of a magnetic tape,flexible print circuit (FPC), electric insulating material, speakervibration board and the like. TABLE C1 Uniformity Film thicknessaccuracy Film surface between Thickness variation (%) structure bothsides of film Example C1 5.5 Porous Good Example C2 5.5 Porous GoodExample C3 5.4 Porous Good Example C4 5.7 Porous Good Example C5 5.5Porous Good Example C6 5.0 Non-porous Good Comparative 10.2 Porous PoorExample C1

As described above, an inventive polyamideimide film can provide a filmhaving an excellent thickness accuracy and a uniformity in aneconomically advantageous manner. A resultant film is has a high heatresistance, a high quality and an economical advantage, which enableutilization in wide range of applications.

INDUSTRIAL APPLICABILITY

As detailed above, by employing the aspects specified in WHAT IS CLAIMEDIS, the present invention can provide a heat-resistant film having acombination of excellent heat resistance, mechanical strength,smoothness, interlaminar peeling resistance and functionalizing agentimpregnating capacity, especially a porous film made from apolybenzazole film, as well as a polymeric solid electrolyte membranehaving a high mechanical strength and excellent ion conductivity,electricity generating performance and gas barrier performance. It canalso provide in an economically advantageous manner a heat-resistantfilm having a satisfactory thickness accuracy and a uniformity.Moreover, a resultant film can preferably be employed in various uses,especially in electric and electronic fields, since it has a high heatresistance, a high quality and an economical advantage.

1) A heat-resistant film comprising at least any one of a polybenzazole,aramid and polyamideimide produced by sandwiching a polymer solutionbetween two supports, introducing a laminate, obtained by converting thepolymer solution into a thin film by a roll, slit or press, into acoagulating bath and peeling at least one side of the supports off inthe coagulating bath to coagulate the polymer solution in the form ofthe thin film. 2) A heat-resistant film according to claim 1 wherein thesupport is a film allowing the poor solvent for the polymer in thecoagulation bath or a vapor thereof to permeate and wherein the poorsolvent or a vapor thereof which has permeated said film is used foreffecting at least a part of the coagulation of the polymer solution. 3)A heat-resistant film according to claim 1 wherein the coagulation bathis a poor solvent for the polymer, or a mixture of a poor solvent and agood solvent, or a solution containing salts in a poor solvent. 4) Aheat-resistant film according to claim 3 wherein the support is a filmallowing the poor solvent for the polymer in the coagulation bath or avapor thereof to permeate and wherein the poor solvent or a vaporthereof which has permeate said film is used for effecting at least apart of the coagulation of the polymer solution. 5) A heat-resistantfilm according to claim 1 wherein the polymer solution is an isotropicsolution. 6) A heat-resistant film according to claim 5 wherein thesupport is a film allowing the poor solvent for the polymer in thecoagulation bath or a vapor thereof to permeate and wherein the poorsolvent or a vapor thereof which has permeated said film is used foreffecting at least a part of the coagulation of the polymer solution. 7)A heat-resistant film according to claim 5 wherein the coagulation bathis a poor solvent for the polymer, or a mixture of a poor solvent and agood solvent, or a solution containing salts in a poor solvent. 8) Aheat-resistant film according to claim 7 wherein the support is a filmallowing the poor solvent for the polymer in the coagulation bath or avapor thereof to permeate and wherein the poor solvent or a vaporthereof which has permeated said film is used for effecting at least apart of the coagulation of the polymer solution. 9) A compositeion-exchange membrane comprising a composite layer formed byimpregnating a heat-resistant film according to claim 1 with theion-exchange resin and a surface layer consisting of an ion-exchangeresin having no micropores formed on both sides of the composite layersandwiching the composite layer. 10) A composite ion-exchange membranecomprising a composite layer formed by impregnating a heat-resistantfilm according to claim 2 with the ion-exchange resin and a surfacelayer consisting of an ion-exchange resin having no micropores formed onboth sides of the composite layer sandwiching the composite layer. 11) Acomposite ion-exchange membrane comprising a composite layer formed byimpregnating a heat-resistant film according to claim 3 with theion-exchange resin and a surface layer consisting of an ion-exchangeresin having no micropores formed on both sides of the composite layersandwiching the composite layer. 12) A composite ion-exchange membranecomprising a composite layer formed by impregnating a heat-resistantfilm according to claim 4 with the ion-exchange resin and a surfacelayer consisting of an ion-exchange resin having no micropores formed onboth sides of the composite layer sandwiching the composite layer. 13) Acomposite ion-exchange membrane comprising a composite layer formed byimpregnating a heat-resistant film according to claim 5 with theion-exchange resin and a surface layer consisting of an ion-exchangeresin having no micropores formed on both sides of the composite layersandwiching the composite layer. 14) A composite ion-exchange membranecomprising a composite layer formed by impregnating a heat-resistantfilm according to claim 6 with the ion-exchange resin and a surfacelayer consisting of an ion-exchange resin having no micropores formed onboth sides of the composite layer sandwiching the composite layer. 15) Acomposite ion-exchange membrane comprising a composite layer formed byimpregnating a heat-resistant film according to claim 7 with theion-exchange resin and a surface layer consisting of an ion-exchangeresin having no micropores formed on both sides of the composite layersandwiching the composite layer. 16) A composite ion-exchange membranecomprising a composite layer formed by impregnating a heat-resistantfilm according to claim 8 with the ion-exchange resin and a surfacelayer consisting of an ion-exchange resin having no micropores formed onboth sides of the composite layer sandwiching the composite layer.